Method and apparatus for gas plating



March 17, 1953 H. G. BELITZ ET AL METHOD AND APPARATUS FOR GAS PLATING Filed May 25, 1949 IN VE/V TORS 01/1 51? FZMWS HANS 6. 1961/72 Patented Mar. 17, 1953 UNITED STATES PATENT 0 F F-ICE .METHOD :AND APPARATUS FORGAS PLATING Hans G. Belitz,.'-l)ayton, and Oliver F. Davis, Troy,

Ohio, assignors to The Gommonwealth Engineering (Jompanymf Ohio, Dayton, Ohio. acoriporation of Ohio ApplicationMay '23, 1949,;Serial1No. 941804 .8 Claims. 1 This invention relates to the art of deposition of metals. More particularly it relates to coating of metal bases. Still more particularly it relates to the plating of objects by the deposition of metal from readily decomposed volatile" metal bearing compounds and apparatus for carrying out the process.

hot object the carbonyl was decomposed and the metal component deposited.

This process has many disadvantages which limit its usefulness. While the chamber is filled with a mixture of inert gas and metal carbonyl vapors, plating only occurs when the carbonylvapor contacts the hot object and general decomposition may take take place, with the result that powdered metal accumulates in the bottom of the chamber.

Further, the deposition rate is very slow and the process requires hours to build up an appreciable depth of metal coating. In addition, the coatings are brittle and adhered poorly to the base metal.

In another process, utilizing quite similar "equipment, the brittleness and poor adhesion has been largely overcome. In this process the metal deposition is carried out in two stages.

After a thin layer of metal is deposited the object is subjected to heat treatment at a temperature of between 500 and 800 F. to desorb the occluded gases. The object was then returned to the chamber and a second coating of the desired thickness over the first layer deposited thereon.

This process, while producing adhering metal coatings, is still a time consuming one. It also requires that the plating cycle be interrupted with consequent loss of materials due to purging the equipment to avoid formation of explosive mixtures of carbonyl gases with air.

Both of .these processes, in addition to the disadvantages mentioned, require that the plating process .be carried out in a closed chamber. This necessitates complicated inlet and egress '2 apparatus if the operation is to be made continuous, or requires that the chambers be large and unwieldy if anything is to be handled o'ther than small objects.

It is an object of this invention to overcome the limitations and disadvantages of the above described processes.

'It is a further object of this invention to provide a process which eliminates the need for 'a complicated pressure chamber and its auxiliary equipment.

A still further object of this inventionis to provide a process wherein small areas can be plated either as initial coatings or "for repair of damaged coatings.

A still further object of this invention is to provide a process which advantageously plates on rotatable objects of considerable thickness.

Still another object of this invention is to provide a process which lends itself to equipment arrangement capable of fast cooling whereby oxidation of plated coats is under direct control of the operator.

It is another object of this invention to provide a process in which the time for depositing any thickness of coating is markedly shorter than heretofore.

It is another object to provide a process which may be operated under either positive or negative pressure conditions.

It is a further object of this invention to provide a process wherein the decomposition gases are quickly removed from the plating area to eliminate contamination of the deposited metal Itis still a further object of this invention to provide a process for continuous and rapid deposition of bright metal coatings by directing the decomposable metal material to the metal surface.

It is a still further object of this invention to provide a simplified method and apparatus for depositing metal from a volatile metal .compound by continuously decomposing the compound and conducting the gaseous product resultant from the decomposition away from 'contact with hot metal in order to avoid contamination and dulling of the bright deposit.

It is still another object of this invention to provide a processwherein the decomposable material is not brought up to a decomposition "temperature before it is in the direct plating zone.

Other and more specific objects and advantages will be apparent to one skilled "in the art as the following description proceeds:

. through some particular range.

ship with a hood adapted to fit in close proximity to the object and designed to have a gas capacity capable of handling the many volumes of gas released by the decomposition of each molecule of volatile compound.

In this process the jet of vapor projected may be formed by mixing an inert gas with the va pors of the metal compound or by atomizing liquid metal compound with a blast of hot inert gas capable of converting liquid droplets to vapors and bringing the vapors to a temperature at which the vapors are on the verge of decomposing and needing only contact with hot metal to free the metal components.

The atmosphere in the vicinity of the surface to be coated is thus made up merely of fresh vapors propelled with force by the blast into the deposition zone and encountering mainly the hot .gaseous decompositio n products which are being removed, by example, as by suction or vacuum drawn on the area surrounding the plating surface.

. Plating material is driven to the plating sur- This inert gas is;

face by a blast of inert gas. fed to the mixing point usually through an annular chamber surrounding a central feed pipe.

Carbon dioxide, helium, nitrogen, hydrogen, the gaseous product of controlled burning of hydrocarbon gases free of oxygen, and the like, have.

been utilized as the gas blast.

We prefer to utilize gas held under pressures of between 30 to 90 pounds per square inch for blasting, but the pressure range is subject to much wider variation, depending upon whether liquid or vapors are being sprayed in a limited area jet toward the plating surface. v

Metals may be introduced as gaseous metal carbonyls or vaporized solutions of certain of the metal carbonyls in readily vaporizable solvents (for example, petroleum ether) also ni-' troxyl compounds, nitrosyl carbonyls, metal hydrides, metal alkyls, metal halides, and the like.

Illustrative compounds of the carbonyl type are nickel, iron, chromium, molybdenum, cobalt, and mixed carbonyls.

Illustrative compounds of other groups are the nitroxyls, such as copper nitroxyl; nitrosyl carbonyls, for example, cobalt nitrosyl carbonyl, hydrides, such as antimony hydride, tin hydride; metal alkyls, such as chromyl chloride; and carbonyl halogens, for example, osmium carbonyl bromide, ruthenium carbonyl chloride, and the like.

Each material from which a metal may be plated has a temperature at which decomposition is complete. However, decomposition may take place slowly at a lower temperature or while the vapors are being raised in temperature For example, nickel carbonyl completely decomposes at a temperature in the range of 375 F. to 400 F. However, nickel carbonyl starts to decompose slowly at about 175 F., and therefore decomposition continues during the time of heating from 200 to 380 F. A large number of the metal carbonyls and hydrides may be eifectively and emciently decomposed at a temperature in the range of 350 F. to 450 F. When working with most metal carbonyls we prefer to operate in a temperature range of 375 F. to 425 F.

Maintenance of the metal objects at temperatures in the general operating range is easily accomplished with numerous heating means, such as radiant heating, electrical resistance heating, induction heating, and the like.

The material to be decomposed is readily brought to the decomposition temperatur by mixing with hot inert gas. Even a fine spray of liquid can be transformed from a liquid at a temperature of F. to a vapor having a. temperature of 325 F. in a fraction of a second, and the vapors being decomposed by contact with a. heated surface having an even higher temperature.

Preparatory to coating base material the metal strip or object to be plated may be cleaned by employing the conventional methods used in the art, comprising electro-chemically cleaning by moving the same through a bath of alkali or acid electrolyte, wherein the strip is made the cathode or anode. Pickling of the metal with hydrochloric, sulfuric or nitric acid, or a combination of acids may also be made as a part ofthe cleaning process, and the strip thoroughly rinsed or washed prior to introduction into the plating apparatus of this invention.

The invention will be more clearly understood from the following description of one embodiment of the apparatus wherein the object to be coated is a rotating shaft.

In the drawings:

Figure 1 is a sectional view diagrammatically illustrating a spray and exhaust apparatus;

Figure 2 is a view of the equipment of Figure 1 along line 22 and showing alternative or cooperative electrical heating means mounted within the hooded area;

Figure 3 is a view along the line 33; and

Figure 4 is a sectional view diagrammatically illustrating a hood capable of enclosing a greater proportion of the surface area of a circular obec Referring to the drawings, there is shown a portion of a lathe [0 having a movable carriage ll associated therewith, in which is mounted a metal shaft I2. The direction of rotation of the shaft is shown by the arrow.

Mounted on carriage l l is a hood I3 having an adjustable head section l4 arranged as further illustrated in Figures 2 and 3. This hood is op eratively connected with a source of vacuum or high capacity exhaust fan, not shown, through conduit [5.

Axially positioned within hood I3 is a pipe l6 which in turn has within it a feed pipe I 1. Each of these pipes is provided with an adjustable end section as shown at lBa and Ila. An anflame, issupplied with combustible: gas; fronta source not shown.

Referring. to Figure 2 there: is shown. a. shaft 12, hood I3, vapor orifice. 19' 'correspondingto their. counterparts illustrated in. Figures 1 and 2.

Mounted on the carriage II is anelectrical resistance coil. 30. through which theshaft. I2

is free to rotate. Coilv 30 is covered by rubber sheaving 3| to prevent. metal from adhering thereto.

It will benoted that inthis instance the heating equipment is mounted. within. the. hooded section.

Conditions of operation with relation to specific plating. operations carried. out in.the above described apparatus will be morezfully set forth in the following examples:

Example I An alloy steel shaft may be positioned-in the lathe [0. The segmentally shaped. hood I 3; sup.- ported by the carriage'may be lowered into close proximity to the. shaft. Nickel. carbonyl; in the form of vapor may be fed through the orifice 19 at a rate of about pound of nickel. carbonyl per minute. The carbonyl vapors may be driven to the surface of the shaft by a blast of carbon dioxidegas. maintained under a pressure of 30 pounds per square inch. The shaft may be maintained at approximately 390 F. by the fiame 22. The hood l3 may be maintained under a slight vacuum of approximately 2 inches of water in the exhaust conduit. At the above flow rate 50 square inches of shaft surface may be plated with a smooth continuouscoating of nickel in less than. one minute.

Example II A wrought. iron. strip which. is to be: coated may be supported on a. non-metallic conveyor, the strip may be moved. in a straight path. and pass under a hood which operates in the same manner as thehood. of Example. I.

This hood differs from; the hood of. Example I only in that it is shaped to fit closely to a flat object. The hood may be positioned in close proximity to the surface of the iron strip.

When the metal has been heated to about 375 F. vapors of iron carbonyl flowing at the rate of 70 cubic feet per hour may be introduced through the nozzle within the hood and projected by the use of nitrogen gas.

The exhaust mechanism may be adjusted to maintain approximately 1 pound positive gas pressure in the plating vicinity.

With the nozzle adjusted to direct iron carbonyl vapors the full width of the iron strip, the strip may be continuously plated with a smooth iron deposit of relatively even thickness.

Example III Copper discs may be supported on the conveyor of Example If and the same equipment utilized for the plating operation.

When the copper discs have been heated to approximately 420 F. vapors of antimony hydride may be introduced through the nozzle within the hood and projected by the use of hydrogen gas supplied under a pressure of 60 pounds per square inch.

The exhaust mechanism may be adjusted to maintain approximately 1 to 2 inches of water negative pressure in the outlet section of the hood.

With a flow rate of vapors of approximately 1100- cubic feet: per 1 hour of antimony :hydride,

small copper discs may be plated withsmooth coating. of antimony ina matter of seconds.

It will be: understood that. while there.- have been given certain specific examples ofthepractice of this invention, itv isnot. intended thereby to. have this invention limited to or circumscribed by the specific details of materials or conditions herein specified, in'view of the fact that this inventionmay be' modified; according to individual preference or conditions without necessarily 'departing' from the spiritv of -this disclosure and the scope of the appended claims.

. 1. The method of plating a steel cylindrical shaft which comprises rotating said shaft,"providing. a protected surface area of said shaft where inert gas atmosphere prevents ingress of air to the plating area, heating saidshaft to a'temperature in therange of 350 F. to 425 F., impinging in a given direction upon said heated surfacearea a vapor stream consisting of carbon dioxide and nickel carbonyl, and'removing the carbon dioxide andnickel carbonyl decomposition products under conditions to maintain mixing of air into the exhaust stream to a minimum, said removal taking place in a direction opposed to that of said given direction.

2'. The method of' plating a metal surface which comprises continuously moving the metal surface to be'plated, providing aproteeted 'surface area of saidmoving metal surface where inert gas atmosphere prevents ingress of air to the plating area, heating said metal surface to: a temperature. of 350 F. to 425 F. before'it enters the protected surface area, impinging in.

a given direction upon saidheated surface area a vapor stream consisting of carbon dioxide and nickel carbonyl, and removing the carbon" dioxide and nickel carbonyl decomposition products under conditions to maintain mixing ofairinto the exhaust streamtoa" minimum, said removal taking' placeina-direction opposed tothat of said given direction.

3. A method of coating a limited metal surface area of an object with metal deposited from a heat-decomposable metal vapor which comprises the steps of restricting the free access of air to the metal surface area to be plated, establishing a source of heat-decomposable metal vapor. heating said metal surface to a temperature in the range of 350 F. to 425 F., impinging in a given direction a blast of said heat-decomposable metal vapor in the form of a jet under pressure onto said limited surface area to be plated, and subjecting said area to localized heating to raise its temperature and cause said impinging metal vapor to decompose and deposit metal on said limited surface area, and removing the decomposition products from the metal plating area, said removal taking place in a direction opposed to that of said given direction.

4. Apparatus for plating a metal object comprising a nozzle, means for supplying heat decomposable metal vapors to said nozzle to deliver a jet of metal vapors under pressure as a blast to a plating surface, means for effecting relative movement between said metal object to be plated and said nozzle, a hood positioned in close proximity to said object and said nozzle and interposed therebetween said hood defining a plating area on said object, heating means for said object, and gas circulating means having an inlet and outlet communicating with said hood for supplying gas thereto and for conducting gaseous decomposition products away from the said plating area.

5. Apparatus for plating a metal object comprising a nozzle, means for supplying heatdecomposable metal vapors to said nozzle to deliver a blasting jet of said metal vapors onto a plating surface, means for effecting relative movement between a said metal object and said nozzle, a hood positioned in close proximity to said object and said nozzle and interposed therebetween, said hood defining a plating area on said object, heating means adjacent to said hood and outside thereof for heating said object, and gas circulating means having an inlet and outlet communicating with said hood for supplying gas thereto and for conducting gaseous decomposition products away from the plating area.

6. Apparatus for plating a, metal object comprising a nozzle, means for supplying heatdecomposable metal vapors to said nozzle to deliver a blasting jet of said metal vapors onto a plating surface, means for continuously moving said metal object before said nozzle, a hood positioned in close proximity to the surface of said object and interposed between said nozzle and said object, said hood surrounding said nozzle and blanketing a limited surface area of the object to define a plating area thereon, heating means mounted within said hood adjacent the surface of said object, a conduit means associated with said hood for the passage of gases therethrough, and exhaust means communicating through said conduit means for removing decomposition products from the plating area.

7. Apparatus for plating a metal object comprising concentric feed pipes for delivering gaseous material, a centrally disposed nozzle arranged within said pipes for delivering heatdecomposable metal vapors in the form of a blast to a plating surface, a hood surrounding the feed pipes and interposed between the feed pipes and the said object and positioned with said concentric feed pipes along the central axis and blanketing a limited surface area of the object to define a plating area thereon, heating means mounted within said hood adjacent the surface of said object, a conduit means associated with said hood, and exhaust means communicating through said conduit means for removing decomposition products from the plating area.

8. Apparatus for plating a shaft which is of cylindrical shape comprising means for continuously rotating said shaft, a hood positioned in close proximity to said shaft and blanketing a segment thereof to define a plating area thereon, a nozzle axially positioned within said hood, said hood being interposed between the said shaft and said nozzle, heating means surrounding said shaft and positioned within the confines of said hood, conduit means associated with said hood, and exhaust means communicating through said conduit means for removing decomposition products away from the plating area, said hood, said nozzle and said heating means being mounted on means for propelling said apparatus laterally along the length of said shaft.

HANS G. BELITZ. OLIVER F. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD OF PLATING A STEEL CYLINDRICAL SHAFT WHICH COMPRISES ROTATING SAID SHAFT, PROVIDING A PROTECTED SURFACE AREA OF SAID SHAFT WHERE INERT GAS ATMOSPHERE PREVENTS INGRESS OF AIR TO THE PLATING AREA, HEATING SAID SHAFT TO A TEMPERATURE IN A GIVEN DIRECTION UPON SAID F., IMPINGING A GIVEN DIRECTION UPON SAID HEATED SURFACE AREA A VAPOR STREAM CONSISTING OF CARBON DIOXIDE AND NICKEL CARBONYL, AND REMOVING THE CARBON DIOXIDE AND NICKEL CARBONYL DECOMPOSITION PRODUCTS UNDER CONDITIONS TO MAIN- 